A conventional television receiver for terrestrial broadcasting will be explained. FIG. 6A is a block diagram of the receiver, and FIG. 6B illustrates the relationship between the frequency of a received signal and the oscillation frequency of a first local oscillator.
As shown in FIG. 6A, a signal is received at an input terminal 1, is filtered to a specific range with an input filter 2, and is amplified to a desired level with an amplifier 3. The output of the amplifier 3 is mixed with a signal from a first local oscillator 5 at a first frequency converter 4 to be converted to a signal of 1900 MHz, a target intermediate frequency signal. The output signal of the frequency converter 4 is then filtered with a band-pass filter (BPF) 6, and is mixed with a signal from a second local oscillator 9 at a second frequency converter 8 to be converted to a signal of 57 MHz. The converted signal is filtered with a filter 10 and controlled in gain with an amplifier 11, and is then released from an output terminal 12.
The received signal, upon having a frequency of 90 MHz as shown in FIG. 6B, has the local oscillation frequency of the first local oscillator 5 become 1990 MHz, a sum of 90 MHz and 1900 MHz. Similarly, the received signal, upon having a frequency of 430 MHz, has the local oscillator frequency become 2420 MHz. The received signal, upon having a frequency of 770 MHz, has the local oscillator frequency be 2670 MHz.
The conventional receiver where the received signal to be first converted into a high intermediate frequency includes the first local oscillator generating a signal of wider range, for example, from 1990 MHz to 2670 MHz.